The present invention relates generally to length measuring instruments having a flexible scale and a scanning unit and specifically to an improved apparatus for controlling the separation between the scale and the scanning unit.
U.S. Pat. No. 4,170,826 discloses a measuring instrument which includes a scanning unit and a flexible measuring scale that is mounted inside a flanged groove to provide for longitudinal adjustment of the scale in the groove. Because the scale is moveable in the groove, there will generally be some degree of play between the groove and the scale. This in turn permits some degree of lateral motion, transverse to the plane of the scale. Such lateral motion may alter the separation between the scale and the scanning unit, thereby inducing measurement errors.